Venom Gland Transcriptomic and Proteomic Analyses of the Enigmatic Scorpion Superstitionia donensis (Scorpiones: Superstitioniidae), with Insights on the Evolution of Its Venom Components

Abstract

Venom gland transcriptomic and proteomic analyses have improved our knowledge on the diversity of the heterogeneous components present in scorpion venoms. However, most of these studies have focused on species from the family Buthidae. To gain insights into the molecular diversity of the venom components of scorpions belonging to the family Superstitioniidae, one of the neglected scorpion families, we performed a transcriptomic and proteomic analyses for the species Superstitionia donensis. The total mRNA extracted from the venom glands of two specimens was subjected to massive sequencing by the Illumina protocol, and a total of 219,073 transcripts were generated. We annotated 135 transcripts putatively coding for peptides with identity to known venom components available from different protein databases. Fresh venom collected by electrostimulation was analyzed by LC-MS/MS allowing the identification of 26 distinct components with sequences matching counterparts from the transcriptomic analysis. In addition, the phylogenetic affinities of the found putative calcins, scorpines, La1-like peptides and potassium channel κ toxins were analyzed. The first three components are often reported as ubiquitous in the venom of different families of scorpions. Our results suggest that, at least calcins and scorpines, could be used as molecular markers in phylogenetic studies of scorpion venoms.

Keywords: enzymes; motifs; phylogenetic analysis; toxins; transcriptome.

Figure 1

(A) Distribution of annotated sequences from the venom gland transcriptome of S. donensis according to Gene Ontology (GO) terms. The category designated by GO as “Biological process” was the most diverse. (B–D) Distribution of the most represented categories within each GO term (GO numbers shown).

Figure 2

Relative proportion (expressed as percentages) of the Pfam domains of the 135 annotated transcripts, which putatively code for venom components found in the venom gland transcriptome analysis of S. donensis. The category Toxins includes putative Na⁺, K⁺ and Ca²⁺ toxin channels peptides; the category NDBPs (Non-Disulfide-Bridged Peptides) includes all possible NDBPs peptides even when no Pfam domain was found; the category Protease Inhibitors includes Ascaris-Type and Kunitz-Type inhibitors; the category La1 includes putative La1-type peptides; the category Enzymes includes all possible peptides with venom enzymatic activity; and the category Other Venom Components includes putative venom proteins and possible CAP peptides.

Figure 3

Sequence alignment of components with identity with sodium channel toxins (cysteine-stabilized α/β motif, CS αβ, indicated as CSab in the toxin names) found in the transcriptome analysis of the venom gland of S. donensis and those that were similar. Unitprot entry numbers precede the toxins’ names: (a) Component sdc14319_g1_i1, translated ORF; (b) CSab-Cer-2 from Ce. squama; (c) CSab-Cer-1 from Ce. squama; (d) CSab-Uro-2 from Urodacus manicatus; and (e) CSab-Iso-3 from Isometroides vescus.

Figure 4

Amino acid sequences of the translated transcripts showing identity with the αKTx subfamily 6, found in the transcriptome analysis of the venom gland of S. donensis, aligned to similar sequences. Unitprot entry numbers precede the species’ names: C5J896 (potassium channel toxin αKTx 6.16); H2CYS1 (αKTx-like peptide); Q6XLL6 (potassium channel toxin αKTx 6.9); Q6XLL5 (Potassium channel toxin αKTx 6.10); Q6XLL7 (potassium channel toxin αKTx 6.8); Q6XLL8 (Potassium channel toxin αKTx 6.7); and P0DL37 (potassium channel toxin αKTx 6.21). The predicted signal peptide is underlined and the mature peptide is in bold.

Figure 5

Sequence alignment of components with identity with Scorpines found in the transcriptome analysis of the venom gland of S. donensis. Peptide sequences were generated by translation from the reported transcripts. For comparative purposes, other known sequences are included (Unitprot entry numbers in brackets). Components sdc34997_g1_i1, sdc14222_g4_i1 and sdc14222_g4_i2; Hge scorpine and He scorpine-like 2 from Ho. gertschi (Q0GY40 and P0C8W5 respectively); Scorpine-like peptide Ev37 from E. validus (P0DL47); CSab-Cer-6 from Ce. squama (T1DMR0); β-KTx-like peptide LaIT2 from Liocheles australasiae (C7G3K3); Antimicrobial peptide scorpine-like 2 from U. yaschenkoi (L0GCW2); and Opiscorpine 3 from Op. carinatus (Q5WQZ7). The predicted signal peptide is underlined and the mature peptide is in bold.

Figure 6

Sequence alignment of components with identity with calcins found in the transcriptome analysis of the venom gland of S. donensis and those that were similar. The transcripts were translated to generate the peptidic precursor sequences. Unitprot entry numbers in brackets. Components sdc9999_g2_i1 and sdc13987_g1_i1; Calcium channel toxin like 20 from Urodacus yaschenkoi (L0GBR1); Hadrucalcin from Hoffmannihadrurus gertschi (B8QG00); ViCaTx1 from Thorellius intrepidus [11]; β-KTx-like peptide LaIT2 from Liocheles australasiae (C7G3K3); Antimicrobial peptide scorpine-like 2 Urodacus yaschenkoi (L0GCW2); and Opiscorpine 3 from Op. carinatus (Q5WQZ7). The predicted signal peptide is underlined; the mature peptide is in bold and the propeptide is in italics.

Figure 7

Sequence alignment of components with identity with Non-Disulfide-Bridged Peptides found in the transcriptome analysis of the venom gland of S. donensis. The sequences derived from transcripts were translated to show the precursor peptidic sequences. For comparative purposes other known sequences are included (Unitprot entry numbers in brackets): CYLIP-Uro-1 and CYLIP-Uro-3 from U. manicatus (T1E6X5 and T1DPA6, respectively); and CYLIP-Cer-2 and CYLIP-Cer-3 from Ce. squama (T1E6W7 and T1E7M2, respectively). The predicted signal peptide is underlined and the mature peptide is in bold.

Figure 8

Phylogenetic tree obtained from the Bayesian analysis of 22 sequences of putative and confirmed calcins from 14 scorpion species belonging to 12 genera and eight families selected from the InterPro database and the available literature. The originally reported names are used (or the UniProt or GenBank accession codes for those lacking a name), followed by the scorpion species (see Supplementary Table S3). Posterior probabilities higher than 0.76 are indicated above the branches.

Figure 9

Phylogenetic tree obtained from the Bayesian analysis of 62 sequences of scorpines and putative scorpines, plus 34 sequences of βKtx or putative βKtx from 34 scorpion species of 22 genera and 10 families, and one sequence as outgroup (αKTx), selected from the InterPro database and the available literature. Terminal names are composed of UniProt or GenBank accession codes and the name of the scorpion species, except for those named as in their original publications (see Supplementary Table S4). Posterior probabilities higher than 0.65 are indicated above/below branches. Clades in red represent sequences from species of genus Tityus; in light green sequences from species of genus Mesobuthus; in orange sequences from species of genus Androctonus; in magenta, sequences from species of genus Chaerilus; in yellow sequences from species of genus Lychas; in purple sequences from species of family Vaejovidae; in light blue sequences from species of family Scorpionidae; in dark green sequences from S. donensis, and in dark blue sequences from several non buthid families.

Figure 10

Phylogenetic tree obtained from the Bayesian analysis of 36 sequences of La1-like peptides or putative La1-like peptides from 23 scorpion species of 18 genera and nine families selected from the InterPro database and the available literature. Terminal names are composed of UniProt or GenBank accession codes and the name of the scorpion species, except for those named as in their original publications (see Supplementary Table S5). Posterior probabilities higher than 0.65 are indicated above branches. Colored clades indicate monophyletic groups of La1-like peptides from scorpions of families Buthidae (red), Scorpionidae (green) and Vaejovidae (blue).

Figure 11

Phylogenetic tree obtained from the Bayesian analysis of 20 sequences of potassium channel κ toxins (κKTxs) from eight scorpion species of four genera and three families; and 12 sequences of potassium channel α toxins and chlorotoxins as outgroup, selected from the InterPro database and available literature (see Supplementary Table S6). Posterior probabilities are indicated above branches. Colored clades indicate the monophyletic subfamilies proposed earlier: subfamily 1 (orange); subfamily 2 (blue); subfamily 3 (green); subfamily 4 (red); and subfamily 5 (purple). The name in red shows κ buthitoxin.